This project will examine pigment gallstone composition and structure with the major aim of determining their method of formation. The specific projects in the coming year will include the following: 1) continuing examination of the microstructure of the various types of pigment gallstones and of cholesterol gallstones of different cholesterol content to ascertain if structure will give clues to the formation of these stones; 2) to examine bile salt composition of pigment and cholesterol stones using high pressure liquid and gas-liquid chromatography; 3) to examine the fatty acid composition of bilirubinate-palmitate stones from the United States and Japan to determine the origin of these fatty acids; 4) to determine if stone composition is a significant factor in determining whether or not radiolucent stones will dissolve in response to chenodeoxycholic acid administration; 5) to determine factors determining the quantity of ionized calcium in bile; and 6) to determine, using discriminant analysis, whether determination of multiple radiologic characteristics of gallstones using oral cholecytographic films will allow separation of pigment from cholesterol stones prior to chenodeoxycholic acid administration.